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130 / MAY–JUNE 2015, VOL. 60, NO. 3
Nutritional Impacts of Different Whole Grain Milling Techniques:
A Review of Milling Practices and Existing Data1
Julie Miller Jones,2 Judi Adams,3 Cynthia Harriman,4 Chris Miller,5 and Jan Willem Van der Kamp6
1 The material in this article is the work of many members of the working group. The views ex-
pressed in this article are those of the authors and contributors and do not necessarily reflect
the positions or policies of the companies mentioned.
2 Corresponding author. St. Catherine University emerita, St. Paul, MN, U.S.A. E-mail: jmjones@
stkate.edu; Tel: +1.651.690.6669; Fax: +1.651.636.2394.
3 Wheat Foods Council, Parker, CO, U.S.A.
4 Oldways/The Whole Grains Council, Boston, MA, U.S.A.
5 Engrain, Manhattan, KS, U.S.A.
6 TNO Food and Nutrition, Zeist, Netherlands.
http://dx.doi.org/10.1094/CFW-60-3-0130
©2015 AACC International, Inc.
This report was produced with the guidance, advise, and review of the AACCI Whole Grains Working Group: Georgie Aley, Grains &
Legumes Nutrition Council, NSW, Australia; Per Åman, Department of Food Science, BioCenter, Swedish University of Agricultural
Sciences, Uppsala, Sweden; Kingsly Ambrose, Department of Grain Science and Industry, Kansas State University, KS, U.S.A.;
Alison Baldwin, Campbell Arnott’s, North Strathfield, NSW, Australia; Anne Banville, USA Rice Federation (retired), Arlington, VA,
U.S.A.; Michelle Bloom, Grains & Legumes Nutrition Council, NSW, Australia; Richard Braem, TH Foods, Love Park, IL, U.S.A.;
Steve Buckholdt, Roman Meal Company, Tacoma, WA, U.S.A.; Jeff Dahlberg, Kearney Agricultural Research & Extension (KARE),
University of California, Parlier, CA, U.S.A.; Brinda Govindarajan, Tesco PLC, U.K.; Joan M. G. Lyon, USDA Center for Nutrition
Policy and Promotion (retired), Washington, DC, U.S.A.; Rajen Mehta, Grain Millers, Inc., Eugene, OR, U.S.A.; Mike Orlando, Sunny-
land Mills, Cardiff by the Sea, CA, U.S.A.; Kathy Wiemer, General Mills Bell Institute of Health & Nutrition, Minneapolis, MN, U.S.A.
Although whole grains have long been revered as health-
promoting dietary components, documentation of these health
benefits beyond their nutrient contribution is much more re-
cent. In terms of nutrients, whole grains deliver important di-
etary components such as magnesium and dietary fiber, both of
which are often low in Western diets. Beyond nutrient content,
the ingestion of whole grains is associated with lower risk of
coronary disease, diabetes, hypertension, overweight, and even
overall mortality (1). As a result, dietary guidance by a variety
of government and health-promoting organizations recommends
the inclusion of whole grain foods in the diet. Most guidelines
call for an increase in whole grain intake by replacing some re-
fined-grain products (2,3). For example, the U.S. 2005 Dietary
Guidelines Advisory Committee (DGAC) recommended that
consumers “make at least half their grains whole” (4). The 2010
DGAC continued this recommendation and added that the
replacement of refined grains be with at least some high-fiber
whole grains (5).
The need to increase consumption of whole grain foods has
increased demand for flours and food products that are wholly
or partially whole grain. In the United States the quantity of
whole wheat flour milled had risen to 5% of the total flour milled
as of June 30, 2011, up from 2% in 2002 (J. Sosland, Milling and
Baking News, personal communication, 2011). According to
Mintel, the number of new product launches touting whole
grains in their formulations was 20 times greater in 2011 than
in 2000 (6). The increase in the number of whole grain products
on the market together with the rise in the consumer demand
for them (7) has created an opportunity to revisit not only
whole grain foods themselves, but also milling processes and
their resultant flours and meals.
Consumers expect that whole grain foods and the ingredi-
ents used to prepare them will deliver anticipated health ben-
efits. Some sources have voiced concerns that milling processes
that separate and combine millstreams may capture fewer whole
grain components and their nutrients, fiber, and microconstitu-
ents than milling processes that never separate millstreams (8).
Such concerns have been expressed despite the fact that sepa-
ration and recombination of millstreams have been practiced
for much of the history of grain milling. Interestingly, the food
intake data linking numerous health benefits and whole grain
foods are based on foods using flours produced through the
recombination of millstreams. There also are concerns about
whole grain foods produced by manufacturers who purchase
separate grain components and combine them at the food pro-
cessing plant (not at the mill). The fear is that they can poten-
tially produce a product that fails to deliver all the whole grain
components because manufacturers or millers may not mix the
millstreams in the correct proportions, either through error or
through an attempt to lessen some of the negative sensory or
baking properties imparted by the bran or germ. Thus, the re-
sulting products would contain components that do not comply
completely with the definition of a whole grain ingredient.
These concerns were brought to the attention of the AACC
International (AACCI) Whole Grains Working Group (WGWG).
As a result, the WGWG assessed milling and other practices
associated with the production of whole grain flours using pub-
licly available, peer-reviewed scientific evidence. Specifically,
the WGWG was interested in the impact of milling practices
and methods of whole grain meal or flour preparation on the
nutritional quality of flours and foods containing these compo-
nents as ingredients. In this review, the term “quality” will en-
compass the impacts of whole grain flour production method
on nutrient contribution to the food; bioavailability of macro-
and micronutrients and phytochemicals; glycemic response;
digestibility, bulking ability, and laxative effects; molecular
weights and viscosities of fiber components such as b-glucan;
and other relevant components or structures that might affect
beneficial health outcomes.
CEREAL FOODS WORLD / 131
To that end, in this article we
will 1) review the AACCI whole
grain definition and various
other definitions that have added
to or refined this definition;
2) highlight the science that
forms the basis of dietary rec-
ommendations to increase con-
sumption of whole grain foods;
3) review the history of milling,
milling terminology, and cur-
rent milling practices; and
4) assess whether techniques
used to create whole grain
foods result in measurable and
practical differences in the nu-
tritional quality of whole grain
flours and foods. Such an analy-
sis will necessitate a review of
stone milling, with and without
separation of millstreams by
sifting; steel-roller milling, with
sifting and recombination of
millstreams at the mill; and
mixing of mill fractions—bran,
germ, and endosperm—in the
proportions found in the native
kernel in a food processing
plant where final products are
made. The product of this latter
process will be referred to as
“reconstituted” whole grain.
Definition of Whole Grains
Whole grains were formally defined in 1999 by an AACCI ad
hoc committee of experts (9). Their goal was to create a defini-
tion of whole grains for use by both processors and consumers.
It reads:
Whole grains shall consist of the intact, ground, cracked
or flaked caryopsis, whose principal anatomical compo-
nents—the starchy endosperm, germ, and bran—are pres-
ent in the same relative proportions as they exist in the
intact caryopsis.
Other scientific and health-promoting organizations and
some regulatory bodies worldwide, including the U.S. FDA and
the 2010 Dietary Guidelines for Americans, have adopted the
essence of this definition. The AACCI definition has provided
the basis for other definitions, which have attempted to make
the wording either more consumer-friendly (10) or to reflect
the realities of milling practices, as in the refinement of the defi-
nition adopted by the European HEALTHGRAIN Consortium
in 2009 (11). All whole grain definitions state that they must
contain the bran, germ, and endosperm in the same propor-
tions as in the original grain.
Health Benefits of Whole Grains
Health benefits associated with the consumption of whole
grain foods, and the cereal fiber they contain, have been dem-
onstrated in numerous epidemiological studies published over
the last 15 years. Cited here are just a few of the many epidemio-
logical studies linking whole
grain consumption with re-
duced risk of a number of
chronic conditions. Specifi-
cally, whole grain consumption
has been associated with lower
risks of diabetes (12–17), stroke
(18,19), overweight and weight
gain (20–23), hypertension
(24–26), coronary heart dis-
ease (27–29), and certain can-
cers (1,30–32) and with lower
mortality for any age (19,33,
34). Consistent links with bet-
ter health outcomes have oc-
curred across widely different
population groups, often with
culturally very different diet
patterns.
Although epidemiological
studies show consistent results
across studies concerning the
health benefits of whole grain
consumption, intervention
studies have produced mixed
results (35,36). Intervention
studies often have small num-
bers of subjects and show the
benefits of ingestion of a spe-
cific whole grain, such as oats
or rye, but not necessarily a
mixture of whole grains or
brown rice (37–40). Even
large randomized intervention trials (41), such as one with
healthy overweight subjects in the United Kingdom, have not
shown improvements in markers of heart disease with in-
creased intake of whole grain foods compared with usual
intake. This study was criticized because the subjects, while
overweight, did not carry known markers of coronary disease
and might not have been at high risk. Thus, recent reviews have
called for more intervention trials. Specifically, Kelly et al. (42)
note that “there is a need for well-designed, adequately-
powered, longer term randomized controlled trials (RCTs)
in this area.” Nonetheless, the positive results of epidemiolog-
ical studies coupled with the fact that whole grains are a dietary
choice with health benefits continue to fuel interest in these
foods (31).
Whole Grains and Milling Terminology and Processes
The majority of epidemiological studies looking at health
benefits associated with the intake of whole grain foods have
been conducted in Western populations, where breads, cereals,
and grain-based foods are primarily wheat based. (Data from
the Scandinavian countries would be the exception.) The body
of evidence for other population groups also points to health
benefits associated with other dietary patterns and whole grain
staples (43–45).
In nearly all of these studies, the whole grains consumed would
have been kernels processed to remove the husk and outer hull
(if a hulled variety). The grains, meals, and flours then would
have been treated with one of the following methods prior to
consumption.
132 / MAY–JUNE 2015, VOL. 60, NO. 3
1) Whole Grains Minimally Processed or Milled: The
grain kernel is left intact or is minimally processed by
breaking or flattening the kernel. In some cases, as in
ancient times, grain kernels are parched and then boiled.
Today, a few whole grain preparations use whole intact
kernels. These include foods such as brown rice and
soaked wheat kernels or oat groats. Examples of whole
grains that have been broken or flattened include cracked
wheat or bulgur and steel-cut, pin-milled, or old-fash-
ioned oats.
2) Whole Grain Flours or Meals Produced at the Mill:
a) Single-Stream Milling: The grain is crushed between
steel rollers or millstones. All parts of the original ker-
nel stay together from the beginning to the end of the
milling process.
b) Multiple-Stream Milling with Recombination: The
grain is crushed, and different grain fractions are chan-
neled into separate millstreams. The millstreams may
be sifted and separated by particle size. Large particles
are often returned to the mill for further grinding to
attain flours and meals with desired and uniform par-
ticle sizes. The last step in the milling process reunites
all the flour streams at the mill so that they have the
original proportions of bran, germ, and endosperm in
the whole grain flour. This process is called recombi-
nation.
3) Whole Grain Flours or Meals Produced Away from the
Mill—Reconstitution: When crushed and separated prod-
ucts of milling, specifically the bran, germ, endosperm,
and minor milling fractions (from the same grain type),
are reunited at the point of use by the food manufacturer,
the process is called reconstitution. Manufacturers must
exercise diligence to ensure that the proportions of the
various components meet the standards set by the AACCI
whole grain definition.
Definitions of recombination and reconstitution are provided
in the sidebar to clarify why the milling industry refers to these
methods in this way.
An In-depth Look at Types of Whole Grain Flour Products
In this section, whole grain meal and flour products obtained
through reconstitution and recombination of multiple mill-
streams are compared in greater detail with those obtained from
single-stream milling, and the contribution they make to whole
grain intake in the United States and other countries with simi-
lar practices is discussed. (Note, in this section the term “flour”
is used to refer to all granulations, including various meals.)
Intact and Minimally Processed Grains. Preparation of
grains for eating may be as simple as removal of the inedible
husk, leaving the kernel with its bran, germ, and endosperm
virtually unchanged. In some grains, such as bulgur (wheat) or
oats, heating or kilning is used to prevent rancidity and main-
tain nutrient quality. Other grains, such as dark varieties of
millet and sorghum, are soaked prior to grinding to lower tan-
nin content and improve digestibility and nutrient availability.
Soaking of corn in water with lime (calcium oxide), called nixti-
malization, improves the availability of certain essential amino
acids and releases the niacin from niacytin, which are both
important for the prevention of niacin deficiency (pellagra).
Soaking the intact grain also may help to hydrate and soften the
grain, shorten the cooking time, facilitate starch gelatinization,
and increase the availability of nutrients. Such factors increase
the use and nutritive contribution of certain grains.
Brown and wild rices, cooked whole oat groats, and wheat
and rye berries (kernels) are examples of traditional cereals that
are eaten as entire kernels. Other techniques may also be ap-
plied to intact grains so they can be utilized for human food.
These include toasting, parching, popping, scoring, or minimal
abrasion (polishing or pearling). Such minimal processing is
necessary to allow grains to absorb water, gelatinize the starch,
shorten the cooking time, release some tightly bound vitamins
and minerals, and increase amino acid availability. This process-
ing also facilitates chewing and digestion and ultimately helps
provide needed nutrients. Examples of minimal processing in-
clude rolling (pressing the grain between heated rollers) of oat
groats or rye berries to make oatmeal or rye porridge, cracking
the grain to make steel-cut (also called pin-milled or Irish) oats,
slight toasting of the cracked kernel to make bulgur (wheat),
parching corn, or popping kernels (as with popcorn). These
procedures may involve heat and pressure.
Although such processes have the capacity to decrease the
concentration of one or more nutrients or phytonutrients, they
also can increase the bioavailability of some nutrients and stabi-
lize nutrients, especially fat-soluble ones, in the bran and germ,
making them less susceptible to oxidative rancidity. Thus, such
treatments can prevent the loss of important vitamins such as
vitamin E and essential fatty acids. Although more whole grains
are eaten after some form of minimal processing than in their
intact whole form, minimally processed forms of whole grains
are still minor contributors to overall whole grain intake (13,14,
27,46,47).
Single-Stream Milled Grains. In single-stream milling, all
the grain placed in the hopper and constituting a single batch
is kept together during the entire crushing process. Grains may
be crushed between millstones or steel rollers. Although some
believe that both the input and output of the mill are from a
single grain variety, this is rarely the case. Usually, a blend of
grain varieties is placed in the hopper prior to crushing to
minimize variations in protein or other quality aspects of the
end products caused by innate differences in varietals or grow-
ing conditions.
Reconstituted and Recombined Defined
Although the definitions of recombination and reconstitu-
tion provided in the Merriam-Webster Dictionary do not
refer to milling directly, they are included here because they
shed light on the common understanding of these words.
Recombine (transitive verb)
1: to combine again or anew
2: to cause to undergo recombination
Recombine (intransitive verb)
1: to undergo recombination
Reconstitute (verb)
1: to restore (food, etc.) to its former or natural state or
a semblance of it, as by the addition of water to a con-
centrate: e.g., reconstituted lemon juice
2: to reconstruct; form again
CEREAL FOODS WORLD / 133
The contribution of single-stream milling to whole grain foods
in Western diets is minimal, and an even tinier fraction comes
from stone mills. This is due, in part, to differences in the ef-
ficiency of stone milling versus roller milling. An average stone
mill grinds ≈2,000 lb of flour/hr, while a steel-roller mill has an
output of ≈3 million pounds of flour/day. Stone milling requires
an experienced operator whose direct monitoring of the mill
ensures that the flour is always between the stones, the flour is
not too coarse or too fine, and the stones are not generating too
much friction and heat (48). Too much friction can not only burn
the flour, the sparks can ignite the flour dust, so the miller must
be present to smell the air and taste the flour to make sure that
the flour is not burnt or causes a fire. In contrast, modern steel-
roller mills are computer controlled.
Whole Grain Flour—Recombined. The majority of whole
grain flours are made by recombining millstreams at the mill.
Although the starting material can be a single variety of grain
raised in a single location, this is rare. Most mills combine a mix
of grains from different locations. This helps mills produce flours
that are consistent in terms of water absorption and other char-
acteristics desired by end users.
In the multiple-stream process, different millstreams are sep-
arated by particle size and other characteristics. Particles that
are too large may be returned to be reground until they reach
the correct size. Before leaving the mill, all the various mill-
streams are recombined to become whole grain flour that will
have the proportions of bran, germ, and endosperm that are
characteristic of the grains in the original batch.
To ensure that nothing is lost during the milling process, grain
millers employ the concept of “mass balance,” i.e., the mass of
grain at the start and end of the milling process is the same
(minus a minor correction for moisture loss that occurs during
processing). In Europe flour may be recombined according to
an established percentage rather than using mass balance. Thus,
whether from single- or multiple-stream processes, the resulting
whole grain flour directly reflects the composite of grains used
at the start of the milling operation. The practice of recombina-
tion was formally recognized by the U.S. Food and Drug Admin-
istration (FDA) in the U.S. Code of Federal Regulations as early
as 1941 (49).
Whole Grain Flour—Reconstituted. Reconstituted whole
grain flours are those made by blending the bran, germ, and
endosperm of a single grain type (e.g., wheat) in the propor-
tions that exist in an intact kernel. Various separated streams
from different process lots, vendors, or batches, which may have
been purchased separately, are joined with their counterparts
away from the mill. Thus, other divisions of a company or other
companies may purchase bran, germ, and endosperm of the
same grain type and reconstitute them into a whole grain flour
to sell or integrate them “at the mixing bowl” to arrive at the
same original proportions of bran, germ, and endosperm char-
acteristic of the grain type (50).
The blending is usually done by end users of the grain, usu-
ally makers of specialty flours or manufacturers of whole grain
foods. The meals, flours, and food products produced in this
way are referred to as reconstituted. To ensure that the propor-
tions of bran, germ, and endosperm are representative of the
intact seed or kernel, reconstituted whole grain flours and meals
must be blended with precision. Some have suggested that safe-
guards are needed to ensure that all the fractions are present
and that the ratios are not “tweaked” to improve bread quality
or other sensory or functional characteristics.
Some countries, such as the Netherlands, have certification
programs for whole grain flours delivered to bakers. In this ex-
ample the Netherlands Bakery Center certification program
includes criteria for flour composition and protocols for an-
nounced and unannounced inspections. The latter is one strat-
egy to verify that whole grains produced by any method of mill-
ing meet the established criteria.
Whole Grains in the Food Supply. Whole grain intake, as
measured in epidemiological studies for determining baseline
consumption or intake during the study, is typically measured
using food frequencies or analogous instruments. As a result,
any nutritional analysis or associations with health outcomes
would reflect the whole grain foods in the marketplace. Thus,
most of the associations linking reduced disease risk and whole
grain consumption are derived from grains processed into flours
produced either by recombination or reconstitution.
History of Milling
Archeological digs have unearthed querns and other milling
devices from ancient civilizations all over the world. Critics of
food processing and modern milling often suggest that separate
millstreams and sifting are modern phenomena. Thus, a brief
review of milling’s long history is important.
In stone milling, grain kernels are often crushed between two
stones—a stationary stone and a stone that rolls or presses on
the grain. Methods for turning the stone have changed over time,
but the net result is a single-stream milling process.
The practice of blending grain varieties and employing sift-
ing and recombining also has a long history. The Greeks and
Romans preferred white bread. The Romans sifted wheat into
seven grades of flour, often using woven horsehair or papyrus
in baskets as sifters. Sifting enabled cleaning of foreign materials
from the wheat and separation of various grain particles.
According to Pliny (.. 70), Roman millers and bakers mixed
varieties to achieve a desired end product. He wrote about com-
bining varietals as follows, “The wheat of Cyprus is swarthy and
produces a dark bread, for which reason it is generally mixed
with the white wheat of Alexandria.” Lighter colored breads
were considered a status symbol in Roman culture. Bread
made from unrefined, unsifted flour was thought to be suit-
able only for the lower classes, slaves, and gladiators. During
the 1st century .., bread made from sifted flour was pro-
duced on a large commercial scale throughout much of the
Roman world.
As early as the 15th century, mills were documented as using
bolting cloths of linen and other woven materials to separate
the white flour from the bran. Old mills had decorated wooden
bran pukers (Kleiekotzer in German), which “puked” bran. This
bran was very rarely added back into the flour (recombined)
because it contained stones and dirt. Instead, it was usually used
as feed.
In colonial New England wheat was milled and sifted into
white flour by removing the bran and middlings. The middlings,
also called “ships stuff” or “red dog,” was used for “ships biscuits.”
Red dog was named after a Native American who traded for all
of the middlings the miller could supply his tribe. Bran was con-
sidered worthless and tossed into streams.
The Industrial Revolution brought many changes, including
multistory water-powered millhouses, rotating sifting reels and
shakers, and woven wire-mesh sifters or silk bolting cloths that
were used to sift refined flour to an even finer particle size. The
process of separating millstreams continued to reflect the desir-
134 / MAY–JUNE 2015, VOL. 60, NO. 3
ability of white flours, while bran, red dog, and other streams
were not highly prized.
Whole grains remained the mainstay of peasant breads. In
most early mills, when the bran and germ fractions were added
back into the refined flour to make whole grain flour, the pro-
cess would have met the definition of recombination rather than
single-stream milling. Thus, recombination is not a new process
and is not associated only with modern steel-roller milling.
Water-driven stone mills built by colonists and pioneers used
sifting techniques (often involving hand sifting, calling sanita-
tion into question) to separate crushed particles by size. Large
particles were reground and recombined after they attained the
desired size. By the beginning of the 19th century, before the
advent of roller mills, complex mills with multiple millstones
and separated millstreams were commonplace.
Few mills today crush grain without separating millstreams,
and even fewer mills use stones.
Impact of Different Milling Processes on Nutrients
Some claim that only whole, intact, or unprocessed grains can
deliver health and nutritional benefits. However, this is not borne
out by scientific data. Studies show that the nutritional value of
whole grains may actually be improved by milling and process-
ing, which increase digestibility and the availability of amino
acids (1), minerals (51), and vitamins (52). Such studies also
suggest that moderate heat and humidity encountered during
milling inactivates enzymes in the flour, which is beneficial be-
cause it inhibits the enzymatic promotion of the breakdown of
lipid components and antioxidant vitamins. Enzyme inactiva-
tion means that flours could potentially have greater vitamin
retention and decreased activity of heat-sensitive antinutri-
tional factors (53).
Whole grain flours are inherently less stable than refined
flours. One website (54) suggests that whole grain flour pro-
duced by grinding between two stones may require refrigeration
because some of the oil pressed out of the germ can be heated
to 60°C or higher, temperatures which can trigger rancidity. In
addition, oil from the germ can gum up the milling equipment,
causing a problem known as “loading.” Nutritionally, the oil on
the stone can result in both the loss and oxidation of fat-soluble
components such as tocopherol and polyunsaturated fatty acids.
Further, the oil can trap some of the flour components.
A study conducted at the French Institut National de la Re-
cherche Agronomique (INRA) showed that stone-ground flours
have higher levels of damaged starch than those produced by
other milling methods (55). Although some damaged starch is
necessary for bread production, high levels not only impair bak-
ing but also change the glycemic response of foods made from
such grains.
Some websites and authors suggest that flour milled between
stones (which has neither been separated nor recombined) de-
livers more nutrients than grains crushed between metal rollers.
This theory is based on the supposition that grains crushed by
stones would not reach a temperature as high as grains crushed
by steel rollers. However, this is only true if the grinding is very
slow and labile components are not exposed to temperatures
that enhance vitamin loss (56).
A study comparing roller, plate, hammer, and stone mills
showed that the highest temperatures were generated when
grinding wheat between stones, with temperatures reaching as
high as 90°C. In contrast, roller mills reached temperatures of
35°C, and plate and hammer mills reached intermediate tem-
peratures within this range. In a study by Prabhasankar and
Rao (57), whole wheat flour obtained from stone- or plate-
ground wheat showed greater loss of total amino acids than
hammer- and roller-milled samples. Unsaturated fatty acid con-
tent, particularly linolenic acid, was lower in stone-milled flour
compared with roller-milled flour. This same pattern of greater
losses in stone-milled flours was seen with both hard and soft
wheats and flours with both weak and strong (high) gluten
(57). These data suggest that roller-milled whole grain flours
deliver a higher level of unsaturated fatty acids than stone-
milled flours.
Studies of milled barley further substantiate findings that
roller milling results in lower temperatures than stone milling.
Complete retention of amylase activity in barley flour after
steel-roller milling indicates there is minimal heat impact
from steel-roller milling. This may be due in part to the high
efficiency of roller mills, which minimize the length of time
flour particles touch the steel rollers (C. Miller, Engrain [for-
merly Buhler Instructor of Milling, Kansas State University],
personal communication, 2011). Bakers are very interested in
the retention of amylase activity because this activity is critical
in baking. Excess heat denatures some proteins and alters other
functional flour components, thus amylase activity may serve
as the “canary in the coal mine,” because too much heat could
signal the potential for problems in baking properties and nu-
trient loss.
Large particle size and high extraction resulting from milling,
especially milling that involves a single pass through a stone
mill, also can affect the bioavailability of iron, zinc, and calcium
(58–61). (This may be especially true for hard wheats, which are
less well crushed using stone milling techniques.) Despite the
presence of many minerals in whole grain foods, their availabil-
ity for absorption in the body may be impaired (62). This can
be a particular problem if grains contain high levels of the po-
tent metal chelator phytate, which impairs mineral bioavailabil-
ity (63). Whole grain cereals and legumes contain ≈600 mg of
phytate/100 g, dry weight.
Impairment of bioavailability is intensified if the minerals are
trapped in the grain matrix, as occurs with large particles. The
effect of particle size has been demonstrated in studies with
corn kernels ground to various particle sizes. Results showed
that large particles were less likely to be acted upon during fer-
mentation by phytase enzymes; as a result, the final product
showed lower bioavailability of many minerals (61). Thus, high-
er phytate levels and larger particles can translate into lower
mineral absorption. A recent study showed that the nutrient
bioavailability of whole grain wheat increased after micromill-
ing (64). Smaller particle size also may impact vitamin avail-
ability. In a study by Yu and Kies (65), B vitamins were found to
be more available from maize bran products when the particle
size was small.
Roller milling may be beneficial compared with stone mill-
ing in terms of dietary fiber. Studies conducted at the Canadian
Grain Commission found higher amounts of total fiber and
cholesterol-lowering b-glucan in barley that was roller milled
than in barley that was stone milled (66–69). This was true for
every barley variety tested. The data also showed that b-glucan
content decreased when the grain was germinated or gluca-
nases were not controlled. Both of these findings provide an-
other argument for improved nutritional function through mild
heat stabilization of millstreams for grains with high enzymatic
activity. Unlike the positive effect of small particle size on vita-
CEREAL FOODS WORLD / 135
min and mineral availability, larger particles of barley had
higher levels of certain fibers such as b-glucan (70). However,
dry milling of oats did not affect the molecular weight of the
b-glucan (71).
When comparing nutrients affected by different milling tech-
niques, it is important to ascertain that differences are ascrib-
able to the milling process and not to different extraction rates
or other aspects of the grain, such as varietal differences. Some
studies showing advantages of stone milling over roller, plate, or
hammer milling do not compare the same extraction rates. In
addition, a comparison of methods must not only look at nutri-
ent content, but also at bioavailability to determine the actual
amount of nutrient absorbed.
Nutritional Advantages of Separated-Stream Milling:
Stabilization and Consistency
Historically, white flour has been favored over whole grain
flour for several reasons. One reason is its ability to create a fine
cell structure and more products; other reasons include its
cleanliness (e.g., no stones, etc.) and stability. In addition, the
unsaturated lipids in the bran and germ portion of whole grain
flour can quickly go rancid.
Modern milling technology enables grain components to be
separated and stabilized. After stabilization they are recom-
bined with the other components from the original kernel. For
example, heat treatment can reduce the activity of a large num-
ber of the lipases in the bran. This is extremely important for
some flours, such as brown rice flour (72). Without stabilization
the availability of brown rice flour would decrease dramatically,
and the cost of all products made from it would increase because
of its short shelf life. Further, the possibility of ingesting oxidized
fats and their free radicals would increase. This would have neg-
ative health consequences, including increased inflammation
and risk of various chronic diseases (73). Thus, for whole brown
rice flour, as well as other flours, the ability to separate the bran
and germ fractions and to stabilize components prior to adding
them back to make whole grain flours is critical for both prod-
uct quality and human health.
Consistency is another advantage of recombination of mul-
tiple streams at the mill. Grains, like all foods, vary widely in
their nutritional and water contents depending on the variety
and growing conditions from place to place and year to year
(discussed below). Selection of an optimal mix of varieties al-
lows mills to produce flours and meals that not only have con-
sistent baking qualities from batch to batch, but that also deliver
consistent levels of macro- and micronutrients. This consistency
enables bakers and other end users of all flours to produce suc-
cessful products from standardized formulations and helps as-
sure consumers a product is safe and nutritious.
Other Key Factors Affecting Nutrients in Whole Grains
Milling method is only one of the potential factors affecting
nutrients in whole grains. In fact, three other factors have a much
more powerful impact on the macro- and micronutrients in
whole grains:
• Differences in grain varietals and cultivars
• Growing conditions (soil, climate, weather, etc.)
• Subsequent processing (baking, extruding, etc.)
Variability in the proximate composition of whole grain wheat
in Germany over a 10 year period (2000–2010) is shown in
Table I (M. G. Lindhauer, personal communication, 2011). The
percentages in Table I are indicative of variation in macrocon-
stituents, revealing a nearly twofold variation in protein, dietary
fiber, and minerals. Similar data for Denmark is provided in
Table II (J. W. van der Kamp, personal communication, 2011).
These data show slightly lower variability in whole wheat flours
in Denmark than was observed in Germany. (The somewhat
lower degree of variability would be expected because the land
and climatic conditions vary less in the smaller country, which
has fairly homogeneous topography and weather.) Similar varia-
tions were observed within species across varieties and growing
regions in an extensive study undertaken as part of the Euro-
pean HEALTHGRAIN Project (74,75).
The vitamin content of whole grains, similar to their proximate
composition, varies by cultivar and growing conditions (76). The
data in Table III show that B vitamins vary two- to threefold, and
loss varies among the vitamins. One study showed 95% of the
pyridoxine in the original wheat kernel was retained in milled
whole wheat flour, and 80–100% of the thiamin was retained.
Any decreases in B vitamin content caused by milling are
then carried through into the bread and other end products
(63). Losses due to milling pale in comparison to vitamin losses
in products made with alkaline leavenings such as baking soda,
those cooked with a lot of water, or those held for long periods
at high temperature, such as occurs on steam tables. For yeast
breads, thiamin losses have been shown to vary from 31 to 56%
(77). However, the type and length of fermentation also impact
nutrient content, availability, and digestibility in whole grain
products (78). Long fermentations increase riboflavin by 30%
and nearly double the thiamin content but reduce the pyridox-
ine content by half. Further, long fermentations and sourdough
may increase mineral bioavailability and improve protein di-
gestibility. Thus, the milling method used may have much less
impact on the final nutrient content than other factors.
136 / MAY–JUNE 2015, VOL. 60, NO. 3
Best Practices in Milling and Manufacturing Support
Increased Whole Grain Consumption
Support for milling and manufacturing processes that main-
tain the integrity and nutritional benefits of whole grain con-
stituents, while enabling increased availability of whole grain
products, facilitates the important goal of increasing whole
grain consumption. Thus, definitions such as the 2009 Euro-
pean HEALTHGRAIN definition that recognize and enfran-
chise current milling practices are important. Specifically, the
HEALTHGRAIN definition states that recombination is accept-
able. It further notes that a whole grain with the loss of a small
amount of the bran carrying undesirable components (e.g., heavy
metals or mycotoxins) may be an important practical modifica-
tion that will result in the objective of improved health better
than rigid adherence to a definition that allows no leeway for
improvements in milled grain safety. The HEALTHGRAIN def-
inition of whole grains states (79):
Whole grains consist of intact, ground, cracked or flaked
kernel after the removal of inedible parts such as the hull
and husk. The principal anatomical components—the
starchy endosperm, germ and bran—are present in the
same relative proportions as they exist in the intact kernel.
• Temporary separation of whole grain constituents dur-
ing processing for later recombination is acceptable.
• Small losses of components—i.e. less than 2% of the
grain/10% of the bran—that occur through processing
methods consistent with safety and quality are allowed.
• Removal of the very outer bran layer—up to 10% of the
bran or 2% of the grain—is acceptable for minimising
levels of undesirable substances such as bacteria, molds,
agrochemicals and heavy metals.
–Milling and processing
• Whole grain foods are almost universally processed to
make them edible and safe for human consumption.
• Whole grain includes grains that have been subjected to
processing but only if, after processing, the germ, endo-
sperm and bran are present in the same, or virtually the
same, proportions as in the original grain.
• Temporary separation of whole grain constituents during
processing for later recombination is acceptable, provided
the proportions of the germ, endosperm and bran are
the same or virtually the same as in the original grain.
• Recombination of bran, germ and endosperm from the
same type and variant of grain in which a component
(bran, germ or endosperm) has been stabilised is allowed
provided that the three components are in the correct pro-
portions.
• Recombination of the endosperm, bran and germ takes
into account that there are variations in the ratio of endo-
sperm, bran and germ between kernels in one ear and
between varieties of one type of grain. Recombination per
grain and per variety will result in some fluctuations in
the ratios of endosperm, bran and germ between batches
of flour and products. There should, however, be no sig-
nificant nutritional losses, and differences should be no
greater than normally found from season to season or
between varieties.
The various bullet points attached to the HEALTHGRAIN
definition of whole grains recognize current industry practices,
noting that temporary separation, stabilization, and recombina-
tion of millstreams as practiced in modern milling and cereal
manufacture are acceptable. The definition also highlights the
variability that exists in grain, so the ratio of bran, germ, and
endosperm is not a fixed standard. The definition allows for
removal of small amounts of the outer layers through tech-
niques such as peeling of very thin outer layers of a grain kernel
to reduce unwanted components and their potential toxicity.
Investigators at VTT in Finland have shown that minimal peel-
ing increases bran utilizability, improves safety (through re-
moval of surface mycotoxins, pesticides, and herbicides) and
does not impact nutrient bioavailability (80).
Research is needed to improve the nutritive quality of grain
and ensure that milling procedures maximize the quality and
nutritive value of milled whole grains. Nevertheless, innovations
to improve both breadmaking potential and availability of nu-
trients from whole grains mandate ongoing vigilance in prac-
tices and refinement of definitions and their application. Such
an effort will encourage change and make certain that rigid ap-
plication of definitions does not prevent adoption of practices
that might improve nutrient bioavailability, product safety, or
product affordability and consumer acceptance. It will also mean
that new techniques and processes that might cause a decrease
in whole grain nutritional value or safety will be scrutinized.
Conclusions
Whole grain flours are produced using different milling tech-
niques. The majority of whole grain flour is produced using
modern milling techniques, usually with steel rollers, through
processes in which a batch of grain is separated into multiple
millstreams, sifted, and then recombined. In other cases con-
stituent millstreams are purchased and combined by a supplier
or end user to achieve a reconstituted whole grain flour or meal
that has the desired functional, food safety, and nutritional prop-
erties. In a very small number of cases whole grain flours are
stone-ground, with the grain kernels crushed between rotating
stones. The techniques of separating, sifting, and recombining
millstreams have been practiced for centuries.
A significant proportion of whole grain flour or meal con-
sumed in Western countries is produced in mills where the mill-
streams are separated and either reconstituted or recombined.
The positive health benefits associated with whole grain con-
sumption are derived from and have been documented in epi-
demiological studies on whole grain foods from grains produced
through modern milling techniques (generally with steel rollers),
in which the millstreams either were recombined at the mill or
grain components were reconstituted to the correct proportions
at the plant. If recommendations for increased consumption of
whole grains are to be met, consumers need to be encouraged to
consume whole grain foods produced by all milling methods.
Existing data comparing single-stream milling and multiple-
stream milling with recombination do not show any strong ad-
vantage for either milling method. Little, if any, publicly avail-
able data exist that show there is a decrease in nutritional value
with multiple-stream milling using either recombination or re-
constitution “at the mixing bowl.” In fact, the separation of mill-
streams, as in the milling of brown rice, allows for highly labile
brans and germs to undergo a stabilization treatment to make
them less susceptible to rancidity. The net result is greater safety,
increased stability, and higher nutrient retention.
Data comparing use of stones and steel rollers in milling, in
most cases, show there is improved nutrient retention, improved
CEREAL FOODS WORLD / 137
protein availability, and higher dietary fiber retention for grains
such as barley when steel-roller mills are used. The alleged high-
temperature destruction of nutrients with steel rollers has not
been documented, and the high throughput rate means the
shorter contact time between the grain and the rollers results in
less loss of unsaturated lipids and greater enzyme activity and
nutrient retention.
Small differences in nutrient amount or availability caused by
differences in whole grain milling practices must also be viewed
in the context of the wider variations caused by differences in
variety, agronomic conditions, and region of cultivation. Such
variability must be considered when comparing batches of flour
prepared by many different methods. Further processing into
breakfast cereals, breads, crackers, and other products can en-
hance or diminish the nutrient quality of the resulting foods.
Research to improve the acceptability and variety of whole grain
products derived from any milling method would be an effec-
tive use of resources. Such efforts could improve whole grain
consumption and, with that, produce an increase in the con-
sumption of the important nutrients and phytochemicals that
whole grains provide.
In summary, the AACCI Whole Grains Working Group sup-
ports increasing whole grain intake through the use of intact
whole grains and grains milled with the use of stones and steel
rollers in single-stream milling, multiple-stream milling where
streams are recombined at the mill, and multiple-stream mill-
ing in which whole grains are responsibly reconstituted “at the
mixing bowl.”
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